Electric switching apparatus



Jam 23, 1951 E. E. ROBINSON 2,539,206

ELECTRIC swrrcnmc APPARATUS Filed Oct. 2'7, 1948 Patented Jan. 23, 1951 morale swrrcnma nrrmrus Eric'Ernest Robinson, North Wembiey, Emma assignor to Rota: Limited, London, England Application October 27, 1948, Serial No. 56,838

1 In Great Britain November 8, 1947 3Claims. (c1. its-mi This inventionhas for its object to provide improved electrical switching apparatus, more particularly forcontrolling an electric motor used for starting an internal combustion turbine, or a jet propulsion or other prime mover, but it may be applied to other analogous uses in which the duration of an operation is required to be automatically controlled. The invention comprises the combination of a manually operable switch having an associated electromagnet for holding it in the closed position, an electromagnetically operable switch under the control of the manually operable switch for controlling the electric engine-starting motor or other apparatus, a two-wayelectrically-heated timing switch, and electromagnetically. operable switching means associated with. the timing switch for controlling the timing switch and the manually operable switch.

In the accompanying drawings:

' Figures 1 and 2 are diagrams respectively illustrating two embodiments of the invention.

Referring to Figure l, which represents an apparatus iorcontrolling a of a turbine, jet-propulsion or other internal combustionlprimemover, this motor isarranged in an electriccircjiit l provided with terminals 2) through wh'ich current from a storage battery (not shownfban be'supplied to the circuit for energising the motor, the latter being provided with field windings, l2. For controlling the motor a there is also arranged in the circuit ill a normally-open switch c which is movable to the closed position by an electromagnet c, this latter being arranged in a circuit l3 which can besupplied with current from the storage battery throughterminals d. The circuit I3 is controlled by a push-button or other convenient manually operable switch I.

In association with the manually operable switch I is arranged an electromagnet l which serves to retain it in itsclosed position, this electromagnet being arranged in a circuit H which is controlled in part by the manually operable switch itself and in part by a switch h operable by an electromagnet i in a circuit l5 which is under the control of the timing switch to be hereinafter described. In addition the circuit it may also be controlled by another switch 1' under the control of an electromagnet 7c connected across'the motor a this switch being opened when (after the engine has been started) the voltage across the motor rises above a predetermined value, or alternatively the electromagnet of this switch is directly responsive to the current in the motor circuit the electric starting motor I I 2 J The timing switch (arranged in a circuit l8 which is closed by the closing of the manually operable switch I) may be of any convenient kind which is operable thermally under the action of heat generated by an electric current. In one convenient form it comprises as shown a bi-metal strip m which is movable between a pair of fixed contacts 1: under the deforming effect created by the heating action or current flowing through the strip, or through an associated heating coil. In series'with the strip m there is arranged in the circuit It a resistance 0 for restricting the current supplied to the strip, and this resistance may be the heating coil above mentioned. Normally the strip-rests on-one of the contacts n. Movement of-the strip to the other contact n is effected by deformation of the strip by heat. Return to the first contact results when the strip is cooled. The contact n on which the strip m rests when cool, is arranged in the circuit I5 containing the electromagnet i. The other contact n is in a circuit [1 containing an electromagnet p for actuating a switch, herein termed a threeway switch having parts I, 2, 3 which respectively control (a) the circuit I5 01' the electromagnet 1' associated with the one contact n, (b) the timing switch circuit l6, and (c) a branch circuit r connected to the circuits I6, H.

The apparatus above described is adapted to operate in the following manner:

Closing of the manually operable switch I completes the circuits l3 and H, and enables these circuits to be supplied with current through the ,terminals d. The current flowing through the circuit l3 energises the electromagnet e, causing the switch 0 to close the circuit Ill, and thereby enabling the motor a to be set in motion by current supplied to the latter circuit through the terminals b. The current flowing through the circuit l4 energises the electromagnet l which serves to hold the manually operable switch I closed. Current also flows from the circuit l3 through the circuit l8 containing the bi-metal strip m and resistance 0, causing the. bi-metal strip to be heated either by the current flowing through it, or by the heating effect of the resistance when the latter is a heating coil. The bi-metal strip m is deformed by the heating action in a relatively short time interval, and is thereby caused to move to its other position in which it co-operates with the second contact n to close the circuit ll of the electromagnet p associated with the three-way switch I, 2, 3. The

latter then' (a) closes the branch circuit 1' through the part 3 and thereby enables current iron: the circuit it to flow, through the branch 3 circuit and energises the electromagnet p independently of the strip m, so that this electromagnet can remain in action after the strip, on cooling, leaves the second contact; (b) opens the circuit ll of the bi-metal strip m through the part I; and (c) closes the part of the circuit ll connected tothe first contact a of the timing switch. With the cooling of the bi-mctal strip m the latter returns at a controlled rate (which may be regulated by enclosing the strip in a heat insulating cover) to the first contact 11. On reachingthis contact it closes the circuit It, and current flowing through this circuit from the circuit it energizes the electromagnet i which causes the switch It in the circuit associated with the electromagnet l of the manually operable switch I to be opened. This electromagnet is thus de-energised and allows the manually operable switch I to open under the action of a spring (not shown) and interrupt the supply of current to the electromagnet e of the motor switch c and to the electromagnet p of the triple-switch I, 2, I which on opening completes the restoration of the system in its initial condition in readiness for a repetition of the cycle of operations.

The modification illustrated by Figure 2 is essentially similar to the example shown in Figure l and diflers only in the following details. Instead of the .three-way switch I, 2, I of Figure 1 there is employed a two-way switch 4 under the control of the electromagnet p in the circuit I1,

and in the position shown this switch closes the branch circuit 1. In its other position it closes the adiacent'part of the circuit it of the electromagnet i. mally closed switch 8 comprising a pair of spring blades l which are separable by the bi-metal strip m through a tappet 1 and push piece 8, either or both of the parts I, 8 being made wholly or in part of insulating material. Also in the circuit ll ofM-the electromagnet i is arranged a normally closed switch I formed in part by the bi-metal strip m. in other respects the example shown in Figure 2 is essentially similar to that shown in Figure 1 and is indicated by the same reference characters.

Initially the various parts of the system are in the condition shown. On closing the manuallyoperable switch I, the motor switch c is closed as in the previously described example. Also current flows through a part of the circuit It, the bi-metal strip m, resistance 0, switch 5, circuit 1' and switch 4, causing the bi-metal strip m to be In the circuit 1' is arranged a norheated. With the consequent deformation of the r strip m the switch 6 is opened and also the switch I is opened (through the push piece 8). The effect of this is to open the circuit 1' and cause the current which previously passed through the switch I to flow through the electromagnet p which is thereby brought into action for moving the switch I to its other position in which it closes the adjacent part of the circuit II. The ohmic resistance of the electromagnet p reduces the heating eil'ect of the current on the bi-metal strip m suflicientlyto allow the latter to return to its initial position where it closes the switch I and completes'the circuit ll. thus bringin electromagnet i into action. The switch It is thereupon -'opened by the electromagnet i and the system brought back to its original condition as in the previously described example.

Whilst the invention is primarily intended for controlling an engine starting motor, or a group of such motors, it may also (as already stated) be applied-to other analogous uses..and-subor- 4 dinate details may be modified to suit different requirements.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. Electric switching apparatus comprising in combination a main electric circuit, an electromagnet arranged in said main electric circuit, a second electric circuit, a manually operable switch arranged to establish and interrupt both said main electric circuit and said second electric circuit, a second electromagnet arranged in said second electric circuit and serving, when energised, to hold said manually operable switch in its closed position, a third electric circuitconnected to said main electric circuit so that current can iiow through said third electric circuit when said manualhr operable switch is closed,- a thermal time switch member connected to said third electric circuit so that said member is responsive to the heating effect of current iiowing through said third electric circuit, and electromagnetically operable switching means controllable by'said thermal time switch member for interrupting said second circuit, and thereby enabling said manualhr operable switch to reopen.

2. Electric switching apparatus comprising in combinations main electric circuit, an electromagnet arranged in said main electric circuit, a second electric circuit, a manually operable switch arranged to establish and interrupt both said main electric circuit and mid second electric circuit, a second electromagnetarranged in said second electric circuit and serving, when energised, to hold said manually operable switch in its closed position, a third electric circuit. con-v nected to said main electric circuit so that our.

rent can flow through said third electric circuit when said manually operable switch is closed, a thermal time switch member connected to said third electric circuit so that said member is movable from its normal position to a, second position by the heating eflect of current flowing through said third electric circuit, a fourth electric circuit arranged to be completed by said member when the latter occupies said second position, a third electromagnet in said fourth electric circuit, a branch circuit whereby current can be supplied to said third electromagnet independently of said member, a fifth electric circuit which is connected by said member. to said third electric circuit when said member occupies its normal position, a fourth electromasnet in said fifth electric circuit, another switch arramed to control said second electric circuit and open able by said fourth electromagnet, and switching means operable by said third electromagnet for controlling said third, fifth and branch electric circuits.

3. Electric switching apparatus comprising h combination a main electric circuit, an electromagnet arranged in said main electric circuit, a second electric circuit, a manually operable switch arranged to establish and interrupt both said main electric circuit and said second electric circuit, a second electromagnet arranged in said second electric circuit and serving, when ener-: gised, to hold said manually operable switch in its closed position, a third electric circuit connected to said main electric circuit so that current can flow through said third electric circuit when said manually operable switch is closed, a thermal time switch member connected 1 third electric circuit so that said member is move- 5 able from its normal position to a second position by the heating eifect of current flowing through said third electric circuit, a fourth electric circuit connected to said third electric circuit, a third electromagnet in said fourth electric circuit, a branch circuit for short-circuiting said third electromagnet, a third switch arranged in said branch circuit and operable by said thermal time switch member, a fifth electric circuit which is connected by said member to said third electric circuit when said member occupies its normal position, a fourth electromagnet in said fifth electric circuit, another switch arranged to control said second electric circuit and operable by said fourth electromagnet, and switch- I.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,826,477 Olpp Oct. 6, .1931 2,339,750 Bartholy Jan. 25, 1944 2,385,616 Eaton Sept. 25, 1945 Sherwood Mar. 1, 1949 

